This invention relates to a process which can be used to obtain a plurality of organic compounds that can be used as chemical intermediates, using particular oleaginous plant species as raw material.
This process can be used to extract, separate and recover fermentable saccharides from said plant species. Through this process, C5-C6 sugars having a low lignin content, which are particularly suitable for fermentation processes, are obtained from the residual lignocellulose biomass of the oleaginous plant material after the seeds have been removed.
The lignocellulose biomass, which is rich in carbohydrate polymers comprising C5-C6 sugars (hemicellulose and cellulose), is an important renewable source of fermentable saccharides. However, because of its complex structure, in order to facilitate the enzyme hydrolysis of the carbohydrates to simple sugars (monosaccharides), it is necessary to break the chemical bonds between their structural components (cellulose, hemicellulose and lignin). Pre-treatments intended to destroy the external structure formed of lignin and hemicellulose, in addition to reducing the crystallinity and degree of polymerisation of the cellulose itself, and to allow access to the cellulose by hydrolytic enzymes, are therefore commonly used.
These pre-treatments may be of a physical, chemical and/or biological nature. The type of pre-treatment used, together with the nature of the substrate, has an effect on the efficiency of the subsequent enzyme hydrolysis. Generally, the pre-treatments are costly, complex and harsh treatments which can bring about degradation of the lignin and hemicellulose and the consequent formation of toxic by-products, which can inhibit subsequent fermentation stages.
In order to improve utilisation of the lignocellulose biomass, it is therefore necessary to develop a pre-treatment which, depending on the type of biomass used, will preserve the hemicellulose rich in fermentable sugars, will make it possible to utilise the by-products and will limit the formation on inhibitors, at a lower cost and with lower energy consumption.
Pre-treatment with alkali is a chemical pre-treatment which is able to remove lignin, with reduced degradation of the sugars. One example of pre-treatment with alkali is described in Patent Application WO 2011/014894 (Annikki GmbH), in which a lignocellulose material such as wheat straw is subjected to a 24 hour treatment with an aqueous solution containing hydrogen peroxide and a base. This process requires the presence of an organic solvent to limit dissolution of the hemicellulose and has the disadvantage that it requires long times and high concentrations of bases, which are removed in the form of salts.
Pre-treatment with alkali has also been combined with physical systems of a mechanical or thermal type, for example extrusion treatments, but with appreciable difficulties associated with the low plasticity and poor flow properties of the biomass. However, for good efficiency these treatments require high temperatures and high concentrations of bases and the use of gelling agents to modify the rheological behaviour of the biomass. Through the process according to the invention, using the above-ground lignocellulose biomass derived from the cultivation of oleaginous herbaceous plants, it is possible to obtain C5-C6 sugars with a high sugar yield through pre-treatment with alkali such as extraction with aqueous solutions at a basic pH, at low temperature and without the need to add additives which modify the rheological behaviour of the biomass. Pre-treatment of the biomass in the process according to the invention in fact makes it possible to effectively remove lignin, acetate, extractables and ash at lower temperatures than in known types of pre-treatment, ensuring a high recovery of hemicellulose and cellulose and avoiding the formation of degradation products having an inhibiting effect such as furfural, hydroxymethylfurfural (HMF) and their derivatives. Also, in comparison with the pre-treatment described above, it requires short times and results in a lower consumption of bases and liquids.